Synchronized timer



May 25, 1948. D.v BARTLETT SYNCHRONIZED TIMER Filed Feb. 5, 1947 2 Sheets-Sheet 1 MMF INVENToR Davia' Bari/eff.

www

El y. 9. 100 l0! /01 la! IM 105 INI" IM M9 l/ l/l Il) IIJ IM [l5 l/ l/7 ll l/9 ATTORNEY May 25, 1948. D; EmR'rLE-rg 2,442,256

sYNcHRoNIzED TIMER Filed Feb. 5, 1947 2 Sheets-Sheet 2 Ey fo.

INVENTOR David Banlez.

BVMW

ATTORNEY Patented May 25, 1948 SYNCHRONIZED TIMER David Bartlett, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 5, 1947, Serial No. 726,584

11 Claims. 1

My invention relates to synchronized timers for controlling electron tubes of the sustained-discharge type, by which I mean, controlled tubes in which the grid or other control-electrode is capable of blocking the initiation of the tube-discharge until a sufficiently positive grid-potential has been reached, at a time when the main anode of the tube is sufficiently positive with respect to its cathode, the tube thereupon establishing an arc between the anode and cathode, and thereafter tending to maintain said arc, regardless of the grid-potential, until the main anode becomes negative with respect to the cathode, and remains negative for a sufficient length of time for the deionization of the tube. Such sustained-discharge tubes include ignitrons and other gas tubes.

Conventional timers, which depend upon the charging-voltage of a capacitor, suiler from thefact that the charging-curve of the capacitor has a iinite and exponentially varying slope. Thus, if eithei' a relay or an electronic tube is triggered from this rising voltage, a slight drift in the critical response-voltage of the relay or tube will have an appreciable effect upon the accuracy of the timer.

It is an object of my invention to provide a step-by-step timing-control which counts or measures a series of voltage-increments or steps which are derived from an alternating-current input-circuit. Thus, by providing a timing-voltage which increases by discrete steps, rather than according to an exponential curve, it is possible to make the tube or relay which responds to said voltage have a critical response-voltage which is in the approximate middle of one of those voltagesteps or increments, so that, even though the relay or tube does suffer slight drifts in its critical respense-voltage, it will still respond to the same step or increment in the timing voltage.

It is an object of my invention to provide an accurate timing-control, which is applicable to a continuous cycle of operations, such as a series of spot-welds, a succession of photographic or X-ray exposures, o1' the iiring of an electronic frequency-changer.

It is an object of my invention to provide a timer in which the timed interval is accurate, and in which the initiations ofa succession of discrete timed intervals is synchronized with the input-frequency.

It is an object of my invention to provide an electronic frequency-converter or inverter-rectier assembly, in which the output-frequency is controlled by such a synchronized timer, so that each half-wave of the output can be adjusted so as to have the same number of rectiiler conducting-periods, in the'same phase-relation to the input.

It is an object of my invention to provide a square-wave generator which is electronically timed, or counter-controlled.

It is a further object of my invention to provide a cycloconverter in which the output-frequency is controlled by such an electronically timed or counter-controlled square-Wave generator. By a cycloconverter, I mean an assemblage of rectier-tubes of the sustained-discharge type, in which the control-electrodes of the convertertubes are each impressed with three voltages, namely,` relatively small rectication-initiating input-frequency peaks, relatively large inverterinitiating input-frequency peaks, and a squaretopped modulator-wave of the desired output-frequency, as broadly described and claimed in an application of Boyer and Hagensick, Serial No. 739,723, led April 5, 1947, and assigned to the Westinghouse Electric Corporation; except that, according to my present invention, an electronically timed, or counter-controlled, square-wave output-frequency generator is provided.

When I designate a circuit as "input" or output, I mean to refer to circuits which, either as a matter of convenience in terminology, or as a.; matter of normal or customary operation, may be1 -designated as input or output, with the understanding that the cycloconverter is capable of transmitting both real and wattless power, with power-transfer in either direction, between the two circuits, so that the so-called input circuit may sometimes receive power fronl the socalled output circuit.

With the foregoing and other objects in view, my invention consists inthe methods, systems, combinations, apparatus and parts hereinafter described and claimed, and illustrated in the accompanying drawings, wherein:

Figure 1 is a diagrammatic view of circuits and apparatus illustrating a basic form of a synchronized timer in accordance with my invention,

Fig. 2 is a curve-diagramshowing the type of stepped control-voltage which is obtained in my timer,

Fig. 3 is a curve-diagram showing the applied impulses or peaked-voltages which are applied to the timer of Fig. 1,

Fig. 4 is a voltage-diagram illustrative of the square-topped output-voltage which is produced by the timer which is shown in Fig. 1,

Fig. 5 is a view showing a three-phase supplyvoltage, which is supplied to a plurality of groups of three-phase rectifier-tubes of a cycloconverter embodying an output-frequency control in accordance with a form of embodiment of my invention as shown in Fig. 10,

Fig. 6 is a voltage-diagram showing the positive and negative voltage-impulses which are applied to the timer of Fig. 10,

Figs. 7 and 8 are voltage-diagrams showing the voltages which are applied to the control-electrodes of the positive and negative groups of cycloconverter-tubes, in one of the output-phases, in the cycloconverter system which is shown in Fig. 10,

Fig. 9 is a curve-diagram showing the succession of positive impulse-voltages which are applied to the timer in Fig. 11,

Fig. 10 is a diagrammatic view of circuits and apparatus, illustrating a complete cycloconvertersystem, controlled in accordance with my counter-controlled square-Wave modulator, for converting from a three-phase input-circuit of sixty cycles or other frequency, to a three-phase output-circuit of a lower frequency, and

Fig. 1l is a diagrammatic View of a different form of embodiment of the timer which is utilized in Fig. 10.

In the simple form of timer which is shown in Fig. 1, a direct-current source, such as a battery E1, is utilized to energize the main anode-Cathode circuit of a vacuum tube VT, which is illustrated as a pentode. The control-grid i4 of the pentode is controlled by means of a peaking-transformer I5 which is energized from a sixty-cycle system or other alternating-current input or control-circuit. The pentode VT is normally non-conducting, but is periodically driven to saturation by the recurrent positive peaks of the peaking-transformer I5. When the pentode VT is driven to saturation, it becomes substantially a short-circuit between the anode-circuit I6 and the cathode-circuit Il of the tube.

The battery-voltage E1, which is applied to the anode-circuit I6 through a suitable resistor I8, is also utilized to charge two serially connected capacitors C1 and C2, of which the capacitor C2 is much the larger. A duodicde DDI is utilized, or equivalent double rectifying-rneans, with its rectifying diode connected in series with the larger capacitor C2, and with its inverting diode 2i connected in shunt around both the rectifying diode and said larger capacitor C2 The anodecircuit iii of the pentode is also continued to a second group of two serially connected capacitors Ci and Cz, which are similar to the capacitors C1 and C2, and which are similarly associated with a duodiode DDZ.

The effect or the circuit thus far described is to increase the voltage on the capacitor C2, or C'z, in a succession of discrete steps or voltage-increments, as shown by the heavy-line curve E2 in Fig. 2. 'Ihe peaking-transformer i5 delivers a succession of voltage-peaks, as shown in Fig. 3, these peaks being applied to the control-electrode of the pentode VT. The negative peaks 23 have no effect upon the pentode, but each positive peak 24 makes the pentode conducting, and keeps it conducting until the postitive peak has subsided to a relatively small value.

Before the rst positive peak 2li, the pentode VT constituted substantially an open circuit on the serially connected capacitors C1 and C2. Neglecting the voltage-drops in the resistor I8 and in the rectifying diode .20, the voltage across the large capacitor Cz, at this time, was

During the time when the iirst positive peak 24 is being applied to the pentode VT, the smaller capacitor C1 is substantially discharged, through a circuit including the inverting diode 2I and the main cathode-anode circuit of the pentode VT. The voltage of the smaller capacitor C1 is thus reduced to a very small voltage, equal to the two tube-drops, this voltage being very small com pared with the impressed battery-voltage E1. 'Ihe larger capacitor Cz is not discharged, at this time. because of the presence of the rectifying diode 20.

Near the termination of the rst positive peak 24, the pentode VT again becomes non-conducting, and the smaller capacitor C1 recharges. Neglecting voltage-drops in the tubes and in the resistor I8, the second charging of the capacitor C1 adds a voltage M( nf-L C1 C2 01+ G1 to the charge on the large capacitor C2. At the end of the second positive peak 24', the recharging of the smaller capacitor C1 increases the voltage on the larger capacitor Cz by the increment Mr 1 `C1 C1 l- C2 01+ C2 The nth step or voltage-increment, on the large capacitor C2, is a maximum when c1 Under these conditions, the nth step becomes If n is large (5 or more), the mates nth step approxi- O.368 0.2 (T WW The sum of the rst "1L steps then approximates the value (c esu?) E,

Actually, however, each step, say the nth step, will be somewhat less than El {11(1 C1 al C? C2 because of the voltage-drops and the leakagecurrents in the tubes. The exact values can be calculated, or determined experimentally, whichever is easier; but the foregoing analysis is sumcient for a iirst approximation for a design. it

is usually desirable to have the ratio of capacitors Cz/Cl of somewhere near the same order of magnitude as the maximum number of steps n which are to be counted or measured by the counter, but the design is not at all critical, and several times this value, either for the number of steps or for the capacitor-ratio, give satisfactory results, Fig. 2 is drawn for a capacitorration Cz C1=10 1. In general, however, the capacitor-ratio will be much larger.

Referring again to Fig. 1, and continuing the description of the apparatus therein shown, it is noted that the voltages appearing across the large capacitors Cz and C'z are applied, respectively. to the control-grid circuits 25 and I25' of two gas tubes GTI and GT2 (or other sustained-discharge tubes), having anode-circuits 28 and 29 which are energized from a second direct-current source E2, through potentiometers 26 and 21 respectively. The anode-circuits 28 and 29 of these gas tubes GTI and GT2 are joined by a commutating capacitor C3. The positive terminal 30 of the second battery E2, and the anode-circuit 28 of the rst gas tube GTI are brought out to an output-terminal indicated by the voltage EM, while the positive battery-terminal 39 and the anode-circuit 29 of the other gas tube GT2 are brought out to a second output-terminal marked EM.

The gas tubes GTI and GT2 are shown .as tetrodes, and their screen or shield-grids are utilized to control the value of the critical voltage which is necessary to be applied to the controlgrid circuits 25 and 25', respectively, before the tubes will break down and become conducting. This control or adjustment is obtained byconnecting the shield-grid circuit 3| to an adjustable potentiometer 32 which is excited from a negative biasing-battery E3.

In the operation of the synchronous timer shown in Fig 1, it will be assumed that the second gas tube, GT2, is conducting current. This condition may be brought about, for example, by momentarily depressing a push button PB which applies the positive voltage of the anode-lead I6 to the control-grid circuit 25', through a resistance 33. While the tube GT2 is conducting, any charge onl the associated large capacitor Cz is leaked off, as grid-current through said tube GT2.

Thus, while the tube GT2 is conducting, its increment-counting capacitor Cz is inoperative. However, the other increment-counting capacitor Cz is operative, building up its voltage, in a series of discrete steps, as already described in connection with Fig. 2. The critical control-circuit voltage of Ithe tube GTI is chosen or adjusted to some value, such as is shown at 34 in Fig. 2, which is somewhere near the middle of the voltage-increment or step to which it is designed to respond, so that the instant of breakdown or iiring of the tube GTI is precisely and accurately timed, in synchronism with the applied peaks 24 of Fig. 3.

When the tube GTI is fired, the voltagewof its plate or anode-circuit 28, with respect to the positive battery-terminal 30, drops from its potentiometer-value 35, as shown in Fig. 4, to substantially the entire negative value of the battery-voltage E2 (neglecting the voltage-drops in the tube GTI), as shown at 36 in Fig. 4. Meanwhile, the voltage of the anode-circuit 29 of the previously conducting tube GT2, with respect to the voltage of the positive battery-terminal 30, had already been substantially at the value 0f 6 the negative battery-voltage Ez, as indicated at 31 in Fig. 4. At the transition-point 3B, therefore, the commutating capacitor C3 momentarily maintains the same voltage-difference (35, 31) between the two anode-circuits 28 and 29, thus momentarily driving the anode-circuit 29 of the previously conducting tube GT2 more negative than its cathode, as shown at 38 in Fig. 4. The time-constant of the commutating capacitor Ca and the potentiometer 21 is made long enough for the delonization of the previously conducting tube GT2. At the expiration of the time determined by this time-constant, the potential of the anode-lead 29 of the previously conducting tube GT2 changes, as shown at 39, from the value 38 to the value 40 which is determined by the setting of the potentiometer 21 in Fig. 1.

The tube GTI is now conducting, and the tube GT2 is not conducting. At the instant 36 when the newly fired tube GTI became conducting, it short-circuited its increment-counting capacitor Cz, so that it ceased counting. At the instant 39 when the previously ring tube GT2 became non-conducting, it removed a similar short-circuit from its increment-counting capacitor C2, and gave the latter its first voltage-increment, as shown at 39 in Fig. 2. At successive positive voltage-peaks 24 (Fig. 3), the capacitor C'z builds up its voltage-steps, as shown by the light-line curve 40' in Fig. 2, until the tube GT2 again breaks down, starting the process all over. In this manner, rst one tube, and then the other. is red.

The two gas tubes GTI and GT2 thus operate as trigger-valves, for cutting ol, first one counter and then the other counter, besides cutting off each other, as each tube becomes conducting.

By adjusting the negative-bias potentiometer 32, which energizes the grid-circuit 3| of the two gas tubes GTI and GT2 in Fig. 1, it is possible to preselect the capacitor-voltage which is required to re each tube. It should be noted that the rst voltage-peak 24, which is delivered by the counter-controlling peaking-transformer I54 after either trigger-tube GTI or GT2 becomes non-conducting, produces the second voltage-increment or voltage-step on the associated stepcounting capacitor C2 or Cz, as the case may be; so that the trigger-tube GTI or GT2, as the case may be, is red after counting one more voltage-increment or step, than the number of timed intervals 24-24 (Fig, 3) between successive peaks of the peaking-transformer I5.

If the same bias is applied to both trigger-tubes GTI and GT2, as shown in Fig. l, the resulting square-topped Waves EM or E'M will be symmetrical, with equal positive and negative half-cycles, as shown in Fig. 4. However, by using difierent bias-voltages on the two gas tubes GTI and GT2, any degree of non-symmetry may be produced. as will be discussed in connection with Figs. 9 and 11.

The timer or counter, as shown, in its basic essentials, in Fig. l, is applicable to many different types of circuits, where repetitive actions are required, under the control of the timer. However. a noveland important eld of application of the timer is in connection with the control of a cycloconverter, as previously indicated.

Fig. 10 shows the application of my electronic timer in the control of a typical cycloconverter. A three-phase supply-line 4I, of sixty cycles, or any other suitable frequency, is utilized to supply energy, as .through a switch 42, to a threephase input-circuit 43 of a cyclo-converter. The

cycloconverter is shown as comprising eighteen main tubes 44, arranged in six groups of three tubes each. Each of the main tubes is of the previously mentioned sustained-discharge type. They are illustrated as gas tubes 44, but they could be ignitrons or any other sustained-discharge tubes,

The cycloconverter tubes 44 are utilized to supply energy to a three-phase output-circuit 45, through paralleling reactors 46A, 46B, and 46C, as more specifically described and claimed in a Boyer application, Serial No. 739,725, filed April 5, 1947, assigned to Westinghouse Electric Corporation.

The eighteen cycloconverter tubes 44 are lettered A, B, and C. in accordance with the three output-phases; with numbers appended, to indicate the input-phases on a six-phase basis. This is done, because there are six tubes, such as AI, A4, BI, B4, CI and C4, connected to each input-phase, and these six tubes are arranged in back-to-back pairs, such as AI-A4, BI-B4, and CI-C4'. The tubes having the odd numerals, such as AI, A3 and A5, are connected to their responsive input-phases in the positive or rectifying direction, that is, with their anodes connected to the supply-circuit; while the evennumbered tubes, such as A4, A6 and A2, are connected to their respective input-phases in the negative or inverting direction, that is, with their cathodes connected to their respective supplycircuits.

The tube-group AI, A3, A may .be conveniently referred to as the positive tube-group for supplying the output-phase A, While the tube-group A4, A6, A2, may be referred to as the negative group for supplying the output-phase A. When the output-currents are at unity power factor, the rectifying or positive tubes supply the positive current-halves, while the inverting or negative tubes supply the negative current-halves in the respective output-phases. When the outputcurrents have a power factor other than unity, the output-current, in each half-cycle, is shared by both groups of tubes for that output-phase.

The control-circuits 50 of the respective cycloconverter-tubes 44 are energized either directly or, as shown, through insulating transformers 5|, which are known in the art. Usually, the control-circuits include also suitable biasing batteries or other sources 52. A separate insulating transformer 5| is shown, for each of the eighteen control-circuits 50 for the main cycloconvertertubes 44. Each insulating transformer 5I is energized by means of a control-tube 53, preferably a gas or sustained-discharge tube, which is energized, in a known manner, from an individual capacitor 54, which is charged by means of charging-transformers 55, energized from the input-circuit 4'3, and unidirectionally charging the several capacitors 54 through rectifiers 56.

The cathodes of the eighteen control-tubes 53 are connected to a common cathode-bus BI.

The control-circuits 51 of the several controltubes 53 are controlled by individual circuits. each serially including a relatively high-voltage input-frequency peaking-transformer 58 and a relatively low-voltage input-frequency peakingtransformer 59, plus a square-wave generator which, in accordance with my invention utilizes my electronic step-by-step counter. The broad combination of two peaking-transformers and a square-wave output-frequency source, is covered by the previously mentioned Boyer and Hagen- 8 ick application, Serial No. 739,723, filed April 'I'he high-voltage peaking-transformers 58 are energized, from the input-circuit 43, through a phase-shifter PH-SI, which is adjusted to phase said peaking-transformers to produce positive peaks at the proper instant for initiating the inverter-operation of the associated main tube 44; while the low-voltage peaking-transformers 59 are connected to the input-circuit 43 through a phase-shifter PH-SZ which is adjusted in phase so as to produce positive voltage-peaks at the proper instant for initiating the rectiiying operation of the associated tube. The, two phase- Shifters PH-SI and PH'-S2 are commonly connected in opposite phase-sequence, and mounted on a common shaft 60, so as to be simultaneously adjustable, as described and claimed in said Boyer and Hagensick application.

In adapting my electronic counter to serve as the square-topped modulator-wave generator for controlling the positive and negative halves of each output-phase of the cycloconvertor, in the form of embodiment shown in Fig. 10, I utilize three counters or counter-assemblies similar to that whichA is described in Fig. 1; the first counter-assembly being set to control the lengths of the positive and negative half-cycles of the first output-phase, while the second and third counter-assemblies are utilized to count off the proper number of steps for spacing the successive output-phases, as will be subsequently described in detail.

In the step-counting modulator-wave generator shown in Fig. 10, I also prefer to utilize an impulsing source which is energized from al1 three of the input-phases, so as to supply three times as many voltage-peaks or impulses as would be obtained from the single-phase peaking-transformer I5 of Fig. 1. Thus, in Fig. 10, I impulse the electronic counter by means of three peaking-transformers 6I, having their secondaries connected in series with each other, and in series with tapped resistors 62. The primary windings of the three peaking-transformers 6I are energized from the different phases of the input-circuit v43, through a phase-shifter PII-S3, which makes it possible to properly adjust the timing of the voltage-impulses of the timer with respect to the input-voltage.

In Fig. 10, the counter-voltage is again supplied by means 0f a battery Ei, which is illustrated as a 325-vo1t battery. Instead of utilizing a single pentode VT for controlling the energization of the two sets of serially connected capacitors C1, C2 and C'i, Cz, as in Fig. l, my Fig. 10 circuit utilizes two pentodes VT and VT', which are energized from the same battery E1, through separate resistors I8 and I8', but which have their respective control-circuits I4 and I4 energized from separate taps 63 and 63 on the peaking-transformer resistors 62, so that the pentode VT responds to the positive peaks or voltage-impulses of the peaking-transformers 6I, while the other pentode VT responds to the negative peaks or voltage-impulses.

'I'he anode-lead I6 of the positively responding pentode VT of Fig. 10 is utilized to energize two serially connected capacitors C1 and C2, having a duodiode DI associated therewith in the same manner as the duodiode 'DDI of Fig. l. In the case of the negatively responding pentode VT', its anode-lead I5' energizes the serially connected capacitors C'i and (3 2, with the duodiode D4 associated therewith in the same manner as the duodiode DD2 of Fig. 1.

The two capacitors Cz and Cz serve as steppedvoltage capacitors for controlling the gas tubes or valves TI and T4 of the first counter-assembly in Fig. 10, these valves operating in the same manner as the valves GTI and GT2 of Fig. 1, and being similarly energized from a battery E2, which is illustrated, in Fig. 10, as being a 100- volt battery.

The same numerals are utilized, for the rst counter-assembly, in Fig. 10, as in Fig. 1, with the exceptions noted, and also with the exception that the two output-circuits are numbered MI and M4, instead of En, and EM. This is because the two counted or measured square-wave circuits Mi and M40! Fig. 10 are utilized to control the output half-cycles of the positive and negative tube-groups AI, A3, A5, and A4, A6, A2, of the nrst output-phase of the cycloconverter, and the numbers associated with the 'modulator or counter-circuits MI and M4 are the numbers associated with two diametricallyy opposite vectors in a six-phase system of vectors.

In Fig. 10, the negative biasing-battery En is indicated as a 50-volt battery. The negativel' bias potentiometer 32 of the first counter-assembly is adjusted to cause the trigger-valves TI and T4 to wait for the proper number of counts or voltage-steps for the correct determination of the desired length of each output half-cycle, in terms of a rectifier conducting-period of the cycloconverter, as will subsequently be explained more fully in connection with Fig. 5.

In Fig. 10, the anode-lead potentiometers 26 and 21 of the first counter-assembly are tapped, at 66 and 61 respectively, to control or release a second counter-assembly.

This second counter-assembly comprises two serially connected capacitors C1 and C2, and an associated duodiode D3, which I energize from the anode-lead I6, and two other serially connected capacitors Ci, C'z, and an associated duodiode D6, which I energize from the anode-lead I6'. The stepped-voltage capacitors C2 and Cz of this second counter-assembly are utilized to energize two trigger-valves T3 and T6, having energizing and controlling circuits which are numbered the same as in the first counter-assembly, except that the output-circuits of the counter are numbered M3 and M6 respectively.

In addition to the equipment which comprises the first counter-assembly of Fig. 10, the second counter-assembly i-s provided with two vacuum triodes or valves V3 and V6, which are shunted across the control-circuits 25 and 25` of the trigger-valves T3 and T6 respectively. When either of these triodes V3 and V6 is cut oi, its associated trigger-valve T3 and T6 responds, in the usual way, to the total voltage which is built up across its associated stepped-voltage capacitor Cz and C'z, as the case may be. However, when the grid of either triode V3 or V6 is posifive, that triode keeps the control-circuit 25 or 25' of the associated trigger-valve T3 or T6 shortcircuited, so that the step-voltage capacitor Cz or Cz, as the case may be, is also short-circuited, so that it does not build up its voltage.

The control-cicults of the triodes V3 and V6 of the second counter-assembly of Fig. 10 are controlled, from the square-topped output-voltage of the first counter-assembly, by means of the tapped points 66 and 61, respectively. Thus, for example, when the trigger-valve TI of the first 10 counter-assembly is cut off, or non-conducting, its anode-lead potentiometer 26 supplies a small positive tapped-off voltage, at 66, to the grid of the triode V3, causing the latter. to be conducting, and hence preventing the operation of the trigger-valve T3 of the second counter-assembly; but when the first valve, Ti, is conducting, it short-circuits the portion oi the potentiometer containing the tap 66, so that the triode V3 is no longer conducting, and the stepped-voltage capacitor C2 of the -second counter begins building up. its voltage-increments which are applied to the control-circuit of the trigger-valve T3.

If desired, the control-circuits of the triodes V3 and V6 may contain a negative grid-bias battery 68.

In Fig. l0, the second counter-assembly has its negative-bias potentiometer 32 adjusted to give the shield-grid circuit 3l a suitable bias so that the trigger-valves T3 and T6 each count the proper number of steps for spacing the second output-phase from the iirstoutput-phase, or a time-period which is equal to one-third of a complete output-cycle, or as close to that value as can be obtained with an integral number of counts.

In Fig. 10, there is a third counter-assembly, comprising the duodiodes D5 and D2, the triggervalves T5 and T2, the triodes V5 and V2, and the output-circuits M5 and M2. Otherwise, the third counter-assembly is identical with the second counter-assembly, which has already been described. The third counter-assembly is controlled, or triggered off, by the tapped points 66 and 61 in the second counter-assembly, in the same manner in which the second counter-as- 1 The six modulator-circuits Ml to M6 of the three counter-assemblies are each utilized to cony trol the control-circuits 51 of three of the control-valves 53. Thus, the modulator-circuit Ml is connected to the secondaries of the three lowvoltage peaking-transformers 59, which are associated with the positive tube-group AI, A3, A5 oi the cycloconverter, namely the group which supplies the positive half-cycles of the first output-phase, A. It will be understood that the secondary of the proper high-voltage peaking-transformer 58 is serially connected with the proper secondary of a low-voltage peaking-transformer 59, and that the secondary of the high-voltage peaking-transformer is connected to the gridcircuit 51 of an individual one of the controltubes 53.

In like manner, the modulator-circuit M4 services or controls the negative tube-group A4, A6, A2, which supplies the negative half-cycles of the output-voltage in the rst output-phase, A. The modulator-circuits M3 and M6 similarly con- .trol the cycloconVerter-tubes having the letter B,

The operation of the counter-controlled cycloconverter, which is shown in Fig. 10 will be more readily understood with reference to the curvediagrams of Figs. to 8.

Fig. 5 shows the three sinusoidal voltage-waves of the three-phase input-circuit 43, the positive halves of the Waves being marked El, E3 and E5, respectively, and the negative half-Waves being marked E4, E6 and E2, in accordance with the six-phase vector sequence, as previously explained. Assuming a unity-power-factor load, the rectifying periods of the cycloconverter-tubes which supply one of the output-phases, such as the tubes AI to A6, are indicated by heavy lines in Fig. 5. It will be understood that the voltages El, E3 and E5 are applied to the anodes of the positively connected rectiers AI, A3, and A5, and that the voltages E4, E6 and E2 are applied to the cathodes of the negatively connected rectiers A4, A6 and A2.

In the particular cycloconverter which has been chosen for illustration in Fig. 10, the cycloconverter-tube" have three-phase rectifier-action, that is, each tube is theoretically capable of conducting for one-third of an input-frequency cycle, when operating as a rectier. It is convenient to refer to the time-period between the crossingpoints 'I0 of successive phases of the positive halfcycles of the input-voltages as one rectiiier operating-period, as indicated in Fig. 5.

Fig. 6 shows the voltage-impulses which are supplied to the secondary circuit of the three peaking-transformers 6I which control the counters in Fig. 10. Thus, in Fig. e, the positive voitage-peaks of the rst phase of the peakingtransformers 6|, may be indicated at 1l, 12, etc., while the intervening negative voltage-peak is shown at 13. The rst positive peak of the next phase would be ld, and the rst positive peak of the third phase would be 15, as shown in Fig. 6. However, it is largely immaterial which phase of the input-voltages furnishes which one of the peaks, in Fig. 6. The really essential point is that there are a succession of positive peaks, 1|, 14, l5, 12, etc., whichare synchronized with the successive positive half-cycles of the voltage-waves, such as El, E3, E5, El, etc., of Fig. 5.

The precise phase-relations between the positive voltage-peaks Il, 14, 15, 12, etc., of Fig. 6, and the input-waves El, E3, E5, E I, etc., of Fig. 5, may be adjusted by means of the phase-shifter PHS3 of Fig. 10. In like manner, the negative voltage-peaks of Fig. 6 are properly phased and synchronized with respect to the negative voltagewaves of Fig. 5.

One advantage of the cycloconverter controlcircuit of Fig. 10 is that it utilizes time-intervals, between the voltage-steps or increments of the counter, which are precisely and accurately synchronized with the successive input-Waves, and which have an accurately iixed time-phase relation thereto, so that the pick-up points of the counters, or the square ends of the output modulator-waves of the counters, may be accurately timed with respect to the several voltage crossingpoints 10, or the successive rectier operatingperiods, whatever they may be. 'Ihese points are accurately determined, because the pentodes VT and VT' of the counter are controlled by the voltage-impulses of Fig. 6, with sufliciently large voltage-impulses to drive the pentodes all the Way to saturation, very suddenly, so that the pentode-response is sharp and accurate; while the trigger-valves Ti to T6 of the counter are also 12 iired on very steep voltage-increments, as explained in connection with Fig. 2.

Figs. 7 and 8 respectively show the squaretopped modulator-circuit voltages Em and Em of the output-circuits Ml and M4 of the iirst counter-assembly in Fig. 10, plotting these voltages with respect to the voltage Eau of the bus 36, which is also the common cathode-bus B' of the eighteen control-tubes 53.

Imposed upon these square-topped modulatorwaves Em and Em of Figs. 7 and 8, are the rectiiication-initiating peak-voltages RI, R3, R5, and R4, R6, R2, of the iirst six low-voltage inputfrequency peak-transformers 59, and the inverter-initiating peak-voltages Il, I3, I5, and I4, IS, I2; of the first six high-voltage input-frequency peaking-transformers 58 of Fig. 10. It must be understood that each rectifier or cycloconvertertube receives only the voltage-peaks having the same number as the rectier.

In Figs. 7 and 8, an exemplary critical responsevoltage of the control-tubes 53 of Fig. 10 is indicated at E53. The intersections of this critical response-voltage with the various rectificationinitiating peaks RI, etc., control the various firing-points 16, etc., for the rectifying actions of the several cycloconverter-tubes.

It will be noted, from the heavy-line outputvoltage curve of Fig. 5, that the positive and negative output-voltage half-waves are exactly identical in Wave-shape, both as to the number of rectier operating-times which are contained in each output half-wave, and as to the input-frequency phase-angle at which each output halfwave commences, this being accurately synchronized with the input-frequency, by reason of the operation of the counter. The starting-point of each output half-phase may be controlled by the phase-adjustment of the phase-shifter PII- S3 of Fig. 10, and this starting-point may be made any point between two successive voltage crossing-points 10 in Fig. 5. This is true, of course, only for particular output-frequencies which correspond to an integral number of rectifier operating-times in each output half-cycle of each output-phase, as will be subsequently explained. In this way, my invention is unique, in accomplishing something which was impossible of accurate timing heretofore.

My invention is also utilizable, of course, to determine output-cycles which are not characterized by the same numbers and phase-relations of the input rectifier operating-times in each output half-cycle, in which case, as in previous cycloconverter systems, there will be some dissymmetry between successive output half-cycles.

The operation so far described has referred to the assumption of a unity-power-factor load, in which the load-current is in phase with the output-voltage. In case of an output powerfactor other than unity, some of the cycloconverter-tubes will fail to have their anodes at a positive potential with respect to their cathodes, at their rectiiier-iiring moment, such as 'l1 in Fig. '7. In such a case, the previously firing cycloconverter-tube will continue to re as a rectiiier, if necessary to the end of the positive voltage half-wave, as at 18 in Fig, 5; and if further necessary, the tube will continue to fire on into the inverter operation of that tube, on the negative half-wave, as indicated at 19 in Fig. 5, until the out-of-phase load-current becomes zero, thus extinguishing the tube, or until the next tube receives an inverter-firing impulse,

13 as at 80 in Fig. 7, if the output-current is that much out'of phase.

The counter-controlled cycloconverter which is shown in Fig. can be 1'tilized with any adjustments of the three count-controlling potentiometers 32, so as to determine the number of counter-steps in each output half-cycle, as determined by the first counter-assembly in Fig. 10, and also the number of counter-steps between successive output-phases, as determined by the last two counter-assemblies of Fig. 10. It is not essential that the total number of counter-steps in a complete output-cycle shall be exactly divisible by three, but if this total number of steps is not exactly divisible by three, then the successive output-phases will be neither uniform in magnitude nor uniform in the number of output-frequency cycles between successive output-phases.

If the count-adjustment of the first counterassembly, in Fig. 10, is such as to count ve impulse-timed steps, or six steps in all (includy ing the rst step which is not responsive to a control-impulse of Fig. 6), and if the count-adjustments of both the second and third counterassemblies are for three impulse-timed steps, or four steps in all, a perfectly balanced three-phase output will be obtained. Thus, if the triggervalve T4 of Fig. 10 fires at, or nearly at, the subsidence of the negative voltage-peak 8l of Fig. 6, as shown at 82 in Fig. 8, the ring of the trigger-valve T4, in Fig. l0, will extinguish the trigger-valve Tl and initiate a positive halfcycle of the modulator-wave Em in Fig. 7, as shown at 83. The trigger-valve Tl will thereupon count the next ve positive voltage-peaks of Fig. 6, namely, the peaks 1|, 14, 15, 12, and 84. At, or near, the subsidence of the fifth positive peak, 84, the trigger-valve Ti will fire, as indicated at 85 in Fig. 7, thereby extinguishing the triggervalve T4 and initiating a positive half-cycle of the modulator-wave FM4, as indicated at 86 in Fig. 8.

The positive half-cycle of the modulator-wave Em, from 83 to 85 in Fig. 7, determines the time during which the rectifier-initiating peaks RI, R3 and R5 may initiate the rectifier-operation of their respective cycloconverter-tubes. The inverter-operation of the tubes, under the control of the inverter-initiating peaks Il, I3 and I5, is independent of the magnitude of the modulatorvoltage Em, because of the magnitude of the inverter-initiating peaks, as explained and claimed in the previously mentioned Boyer and Hagensick application.

It will be noted that the positive, or rectification-initiating, half-cycle of the modulatorwave Ein in Fig. 7 is initiated at the termination of a negative counter-controlling voltagepeak 8|, in Fig. 6, but that the time duration of this positive half-wave of modulator-voltage Em in Fig. 7 is determined by the counting of Five positive voltage-peaks in Fig. 6. As shown .in Fig. 6, the time-displacement between a negative counter-controlling peak 8| and the next positive counter-controlling peak 1I is sixty input-frequency degrees, or just one-half of the time-interval between two successive positive countercontrolling peaks, such as 1l and 14.

The alternation between a lnegative-peak control, and a positive-peak control, therefore results in the counting of a time-interval equal to a half-step less than the total number of positive-peak counts. Thus results, in the assumed case, in a rectication-initiating modulator-control of exactly four and a, half impulse-controlled' lobtain the necessary half-step time-period.

14 counter-intervals. Since the counter-intervals are equal to the rectifier operating times, there are thus exactly four and a half rectifier operating-times in each half-cycle of the output-frequency, in Fig. 10. On this basis, a total output-cycle equals exactly nine counter-intervals, and the displacement between successive outputphases is therefore exactly three counter-intervals. In Fig. 8, if the point 82 is the tiring-point Afor initiating the first output-phase, which may be designated A, the firing-points for initiating the other two output-phases would be as indicated, in dotted lines, at 81 and 88 in Fig. 8.

It will be noted, from Figs. 5 to 8, that the successive output-frequency rectification-permitting times, for both the positive and negative tube-groups of the cycloconverter, are always terminated at exactly the beginning of a rectifier operating-period of its own polarity. Thus, the positive-tube rectiiication-permitting output-frequency period is initiated at the point 83 in Fig. 7, which very quickly follows the point 82, in Fig. 8, which corresponds to the negative voltage-crossing point 82 in Fig. 5. This rectification-permitting output-frequency period terminates at the point 85 in Fig. 7, which corresponds exactly to the positive voltage-crossing point 85 in Fig. 5. This phase-coincidence is adjusted by means of the phase-shifter PII- S3 of Fig. 10. Any other phase-relationship could have been lutilized, with obvious changes in the each half-cycle of each output-phase.

Between the positive voltage-crossing point 85, f

after which no more cycloconverter-tubes of the positive group will be red, in that output halfcycle, and the next negative voltage-crossing point 89, before which no cycloconverter-tube of the negative group could be tired, there is a timeinterval of one-half of a rectifiervoperating-period, as shown in Fig. 5. This provides a timeinterval in which the voltage El can drop to zero, at in'Fig. 5, on the last positive-group rectier which was red in the output half-cycle in question. In this manner, a certain timeinterval is provided, whereby the simultaneous rectifier-operations of positive and negativegroup tubes may be avoided, as more particularly described and claimed in a Boyer and Hagensick application, Serial No. 739,724, filed April 5, 1947, and assigned to the Westinghouse Electric Corporation.

As previously intimated, itis possible, with my counter, to produce square-topped modulatorwaves having shorter positive periods than negative periods, and in this manner, an interval longer than one-half of a rectier operating-time may be provided, between the rectication-nitiating firing of tubes in the positive and negative tube-groups, as described and claimed in the lastmentioned Boyer and Hagensick application.

Such a variation is shown in the counter-control modulator-wave generator which I have shown in Fig. 11.

Fig. 11 also shows a further variation in the counter-mechanism of Fig. 10, in regard to the impulsing of the counter. In Fig. 10, the counter was impulsed by a three-phase impulsing-system, and it was necessary to distinguish between the positive and negative impulses, in order to In Fig. 11, my counter is impulsed by a six-phase impulsing-system, which is obtainedn with three peaking-transformers 8l', each having two secondary windings, which are connected 'to loading resistors 9| through oppositely directed rectiiiers 92 and 93 respectively. The two secondaries of each peaking-transformer 6|' are connected in opposite polarity, and all six secondaries are connected in series with each other, and in series with the resistor 62, which is tapped, at 63, to control the pentode VT, only one pentode being utilized in the particular counter-system which is shown in Fig. 11.

In Fig. 1l, there are six counter-assemblies, all energized from the anode-lead I6 of the same pentode VT. The rstcounter-assembly has two trigger-valves marked Ti and T|", the second counter-assembly has two trigger-valves T3' and T3", the third has T5 and T5", the fourth has T4' and T4, the fifth has T6' and T6", and the sixth has T2' and T2".

The irst counter-assembly, having the trigger-tubes Tl' and Tl" in Fig. ll, is similar to that which has been described in connection with Fig. 1, except that the screen-grid control-circuits for the two trigger-tubes are separated. The trigger-tube Ti' has a screen-grid circuit 3|' which is energized from the negative-bias potentiometer 32, as in Fig. 1; but the triggertube Tl" has a separatescreen-grid circuit 3|, which is connected to the screen-grid circuit 3| through a potentiometer 94, which is energized from a separate negative biasing-battery 95, so that a predetermined, but adjustable, negative potential-difierence may be maintained :between the screen-grids of the two trigger-tubes. The result of this connection is that the trigger-tube Tl counts a smaller number of steps than the trigger-tube TI. The steps counted by Tl are determined by the negative-bias potentiometer 3'2, and the number of additional steps counted by the trigger-tube TI" is determined by the potentiometer 94. The anode-circuit of the trigger-tube TI' is utilized as `the modulatorfrequency output-circuit Mi', corresponding to the output-circuit Mi of Fig. 10. The anodecircuit potentiometers 26 and 21 of the two trigger-tubes Ti and T|" are tapped, at 66 and 61, to control the starting and stopping of the second and fourth counter-assemblies, as will be subsequently described.

The second counter-assembly, having the trigger-tubes T3' and T3" in Fig. 11, is similar to the counter-assembly which isl shown in Fig. 1, except for the addition of the tapped points 66 and 61, and the addition of the operation-controlling triodes V3 and V3", which are associated with the respective trigger-tubes T3 and T3". The grid-circuits of the counter-controlling trlodes V3' and V3" are energized from the tapped circuits 66 and 61 of the iirst counter, as shown. The two trigger-tubes T3 and T3" of the second counter-assembly have a common screen-grid circuit 3|, which is controlled by a negative-bias potentiometer 32 which is adjusted to count the proper number of cycles for Athe spacings between the output-phases. The anodecircuit of the trigger-tube T3 is utilized as the modulator-frequency output-circuit M3', corresponding to the output-circuit M3 of Fig. 10.

The third counter-assembly, having the trigger-tubes T5' and T5" in Fig. 11, is similar to the counter-assembly of Fig. 1, except for the addition of the counter-controlling triodes V5' and V5", which are controlled from the tapped circuits 66 and B1 of the second counter-assembly of Fig. l1. The anode-circuit of the triggervalve T5' is utilized as the modulator-circuit out- The anode-circuit of 16 put lead M5', corresponding to the output-lead Mi of Fig. 10.

The fourth counter-assembly, having the triggertubes T4 and T4" in Fig. 11, is similar to the second counter-assembly of Fig. ll. Its counter-controlling triode V4', which controls the trigger-valve T4', is energized from the tapped circuit 66 of the first counter-assembly o! Fig. 11, so as to respond to the functioning of the rst trigger-tube TI'. The counter-controlling triode V4'", which controls the other trigger-tube T4" of the fourth counter-assembly, is controlled from the Atapped point 61 'of the ilrst counter-assembly. so as to be responsive to the operation of the second trigger-tube Ti" of said rst counter-assembly. The step-counting adjustment of the fourth counter-assembly is so adjusted, by means of the negative-bias potentiometer 32, that the trigger-tubes T4 and T4 count the number of steps necessary for the Spacing between the positive and negative halfcycles of 'the iirst output-phase, which I have designated as the A-phase. In other words, this timing is equal to one-half the total number of steps which make up a complete output-cycle. the trigger-tube T4 is utilized as the modulator-frequency output-lead M4', corresponding to the output-lead M4 of Fig. l0.

The fifth and sixth counter-assemblies oi Fig. 11 are dependent upon the fourth counter-assembly, to provide the negative-tube modulatorwaves of the output-phases B and C, in the same manner that the second and third counter-assemblies are dependent upon the iirst counterassembly, to produce the positive-tube modulatorwaves of the output-phases B and C. The anode-leads of the tubes TB and T2' are utilized as the modulator-circuit output-leads M6' and M2', corresponding to the output-circuits M8 and M2 of Fig. l0,

The operation of the step-counting modulatorcontrol of Fig. 11 will -be understood from the foregoing explanations, and also by reference to Fig. 9, which shows the counter-controlling voltage-impulses which are applied to the pentode VT of Fig. l1. Although the assembly of Fig. l1 can be operated with any adjustment of the various count-controlling negative-bias potentiometers 32 or 94, it will be illustrated as if the counter-settings are so adjusted that the iirst trigger-valve TI' responds to 9 counts, thus measuring 8 time-intervals of the counter, while the second trigger-valve Tl" responds to ll counts, or l0 time-intervals of the counter. This gives a total of 18 counter-intervals for a complete output-cycle. The trigger-valves T4 and T4" respond, therefore, to 10 counter-steps, or 9 counter-intervals, so as to provide the correct timing for 180 output-frequency degrees. The other four trigger-valves of Fig. 1l each respond to 7 counter-steps, or 6 counter-intervals, to provide the correct spacings for 120 output-frequency degrees.

In Fig. 9, the irst twenty counter-controlling voltage-peaks or impulses are shown, marked from 100 to 119. If the rectification-permitting modulator-frequency period, for the positive cycloconverter-tubes Ai, A2, A3, serving the first output-phase, A, began near the end of the first impulse, |00, in Fig. 9, as shown by the point |20, then this rectification-permitting period would terminate near the end of the eighth impulse thereafter, namely the impulse |08, as indicated at 12|. A rectication-blocking period will 17 then follow, for this same positive group of tubes, extending through the next ten impulses, or to a point |22, near the end of the impulse H8. The second and third counter-assemblies of Fig. 1l will then count off six steps from the point |20, yielding the point |23, and six more steps from the point |23, yielding the point |24, marking the beginnings of the modulator-frequency rectification-permitting periods for the positive tubes BI, B3, B5 and Cl, C3, C5, which serve the second and third output-phases respectively. The fourth counter-assembly in Fig. 11 will measure olf nine steps from the point |20, determining the point |25 at which there commences the rectificationpermitting modulator-frequency period for the negative tube-group A4, A6, A2 which serves the first output-phase, A. The fifth. counter-assembly of Fig. 11 will count six steps from the point |25 yielding the point |26, marking the beginning of the modulator-frequency rectification-permitting period of the negative tube-group B4, B6, B2. The last counter in Fig. 11 will measure off six more steps, not shown in Fig. 9.

The following additional general discussion is applicable to my invention. If we have a threephase input-circuit, and if we obtain three positive counter-impulses and three negative counterimpulses during each input-cycle, as in Figs. 6 and l0, the time-intervals or steps between the positive impulses will be V2 of an interval out of phase with the time-intervals or steps between the negative impulses. If we distinguish between the positive and negative impulses, as in Fig. l0, we have a counter-system which is capable of measuring or counting an integral number of steps or time-periods, if the measured period is terminated by an impulse of the same polarity as the initiating impulse; but if the measured period is terminated by counting impulses of a pularity opposite to the polarity of the impulse which initiated the measured period, then the number of steps or time-periods will be decreased by a half-step, or one-sixth of an input-cycle, or 60 input-frequency degrees.

If we derive a six-phase counter-controlling circuit from a three-phase input-circuit, and if we eliminate the negative impulses, as in Figs. 9 and 1l, we still have a counter-system which is capable of determining a time-period or step which is one-sixth of an input-cycle, or 60 inputfrequency degrees.

If we had derived a twelve-phase counter-controlling circuit from a three-phase input-circuit, still eliminating the negative impulses, we would have had a counter-system capable of determining a time-period or step which is one-twelfth of an input-cycle, or 30 input-frequency degrees. With an impulsing-means or system in which each impulse is about 30 degrees in width, at its base, 30 cycles is about the smallest time-period which can be counted.

By using less than three phases for impulsing the counter, as in Fig. l, or by omitting the negative-impulse response, the counter could be made to respond to a smaller number of time-periods or counts, during each input-cycle.

,In regard to the rectifier-operation, given a three-phase supply-cincuit, it is possible, by suitable rectiiier-connections, to obtain rectifier-operation having 2, 3, 4, 6, or even more, operatingtimes per input-cycle, defining an operating-time as the period between successive crossing-points of the positive voltage half-waves of the inputphases which are effectively applied to the several rectiflers.

These considerations are useful in determining the conditions under which a perfectly balanced three-phase output may be obtained, with exactly output-frequency degrees between phases. and with exactly output-frequency degrees between the beginnings of the positive and negative portions or half-cycles of each phase. One of the advantages of my invention is that both the positive and negative portions (or half-cycles) of each output-phase may be precisely timed so as to begin at the same phasepoint of an input-frequency operating-period of a rectifier-tube. thereby obtaining exactly uniform output half-cycles, in all of the outputphases. It should be understood, of course, that, for many, or even most, applications, it may not be necessary to operate my invention with such refinement, because the output half-cycles are vnecessarily somewhat non-sinusoidal, so that there are harmonics present anyway, and frequently no great harm is caused by more or less departure from )exactl 120-degree output-phase relations, or by more or less inequality in magnitude, rin the output-phases or in the output half-cycles, the harmful effects of which are only a slight increase in the heating of the outputcircuit motor, and double-frequency torquepulsations due to the single-phase power-component. Many motors Iare quite capable of operating satisfactorily with a rather considerable degree of unbalance, and with considerable harmonies in the voltage wave-form. This ls particularly true of motors (not shown) having squirrel-cage wind-ings or damper-windings.

However, it is useful, for some applications or load-circuits, to know the conditions for obtaining a perfectly balanced three-phase output, which is possible with my invention. IThere are two cases to be considered.

Case L When there are an vodd number (as 3) of rectifier operating-times per input-cycle, the rectifier operating-times of the positive group of tubes (or tubes operating on the positive halfcycles of the successive phases of input-voltage) are displaced from the operating-times of the negative tube-group, in each output-phase, by one-half of an operating-time, (paying no attention to which rectifier-phase is which, but simply noting the crossing-points of successive voltage-waves which are applied to the positive and negative tube-groups, respectively). Hence a complete output-cycle includes an odd number, say (21H-l), of operating periods, so that 180 output-frequency degrees equals (n+1/2) operating-periods, where n, is an integer, subsequently to be defined more definitely. The counters will 'count or measure m timed intervals, which We will call steps, for each output-frequency rectifying-permlitting period, and (m-l-d) steps for each output-frequency rectiiying-blockng period, and p steps for the time-lags between the outputphases, where d and p are integers, 'and m is veither an integer or an integer plus l/i, as has previously been explained. These integers Will subsequently be defined more definitely.

The number of operating-periods in one output-cycle is Where c is the ratio of the length of a rectier operating-time to the length of the step or timeperiod between impulses of one polarity, winch is measured or counted by the counter.

c= 1=the number of counter-periods per rectifier operating-time k=any integer greater than zero p=2k1=1, 3, 5, 7, 9, 11, etc.

d=any positive inte er (including zero), which will make the measure count, m, greater than zero.

Thus, in Fig. 10, if we choose k to equal 2, and (dr-) difference between the rectification-permitting and reotiiication-blocking output-frequency periods, we will have (11:3) counterintervals between successive output-phases, and (2n-91:9) rectifier operating-times for a complete output-cycle, and (m=4 and 1/2) counterperiods per output half-cycle.

Another important example is where a sixphase counter-controlling circuit is used, as in Fig. 11, and where the counter is used with a three-phase rectifier of the type shown in Fig. 10. Under these conditions, Equation 1 is satisfied by the following constants:

c=2=the number of counter-periods per rectifier operating-time =any integer greater than zero p=4Ic-2=2, 6, 10, 14, 18, 22, etc. n=3k-2=1, 4, 7, 10, 13, 16, etc.

(3, 6, 9, 12, 15, 1s, etc.)-

d=any even number (including 0), which will make the measured count, m', greater than zero.

Thus, in Fig. 11, if we choose k to equal 2, and (d=2) counter-intervals for the difference between the rectification-blocking and rectificationpermitting output-frequency periods, we will have (p=6) counter-intervals, or 3 rectiiier operating-times, between successive output-phases; and (3=18) counter-intervals or (2n+1=9) rectifier operating-times for a complete output-cycle; and (m'=8) counter-intervals for each rectificationpermittng output-frequency period; and

counter-intervals for each rectification-blocking output-frequency period; and (18/2=9) counterintervals between the beginnings of the rectification-permitting square-wave half-cycles of the positive and negative tube-groups of any outputphase.

Case 2.-When there were an even number (as 2, 4 or 6) of rectifier operating-times per input-cycle, the operating-times of the positive and negative tube-groups would be in phase with each other (paying no attention to which rectifierphase is which, but simply noting the crossingpoints of successive voltage-waves which are applied to the positive and negative tube-groups, respectively). Hence a complete output-cycle would include an even number, say 2N, of operating-periods, so that 180 output-frequency degrees equals N operating-periods, where N is an integer, subsequently to be defined more deflnitely. The counters would count or measure M steps or counter-intervals for each output-frequency notifying-permitting period, (M+D) steps for each output-frequency rectifying-blocking period, and P steps for the time-lags be- 20 tween the output-phases, where D and P are integers, and M is either an integer or an integer plus 1/2, as has previously been explained. These integers will be defined more definitely.

The number of operating-periods in one output cycle is 2M +D 3P 2NT-n 2) where C is the ratio of the length of a rectifier operating-time to the length of the step or timeperiod between impulses of one polarity, which is measured or counted by the counter.

An example would be where three-phase impulses are applied to the counter, and where the rectifiers have six-phase operation. Under these conditions, Equation 2 would -be satisfied by the following constants:

C==the number of counter-periods per rectifier operating-time P=any integer greater than zero= 1, 2, 3, 4, 5, 6, etc.

N=3P=3 6, 9, 12, 15, 18, em.

make the measured count, M, greater than zero.

Thus, if we should choose (P=5) counterintervals, or (5 2=10) rectifier operating-times, between successive output-phases, and (D=2) counter-intervals, or (2 2=4) rectifier operating-times, for the difference between the rectification-blocking and rectification-permitting output-frequency periods, we would have (3P-:15) counter-intervals, or (2N=6P=30) rectifier operating-times, for a. complete output-cycle; and (M =6 and lA) counter-intervals, or 13 rectifier operating-times, for each rectification-permitting output-frequency period; and (M +D=8 and l/2) counter-intervals, or 17 rectifier operating-times, for each rectification-blocking outputfrequency period; and (l5/2:7 and 1/2) counter-intervals between the beginnings of the rectification-permitting square-wave half-cycles of the positive and negative tube-groups of any output-phase.

Another example would be where six-phase impulses are applied to the counter, and where the rectiers have six-phase operation. Under these conditions, Equation 2 is satisfied by the following constants:

C"=1=the number of counter-periods per rectifier operating-time K'=an integer greater than zero Pf=2 =2, 4, 6, s, 10, 12, etc.

=3K=3, ,6, 9, 12, 15, 18, etc.

l M=3K'-2-=(3, 6,9, 12, 15, 18, etc.) -l

D=any even number (including O), which will make the measured count, M', greater than zero. Thus, if we should choose K to equal 4; and

(D=2) counter-intervals (or rectifier operatingtimes) for the difference between the rectification-blocking and,rectiiication-permitting outputfrequency periods, we would have (P'=8) counter-intervals (or rectifier operating-times) between successive output-phases; and (3P=24) counter-intervals, or (2N'=24) rectifier operating-times, for a complete output-cycle; and (M=1l) counter-intervals (or rectifier operating-times) for each rectification-permitting output-frequency period; and (M'+D'=13) counter-intervals (or rectiiier operating-times) for each rectification-'blocking output-frequency period; and (24/2=12) counter-intervals between the beginnings of the rectification-permitting 21 square-wave half-cycles of the positive and negative tube-groups of any output-phase.

While I have shown certain specic forms of embodiment of my invention, and have described its mode of operation in accordance with my present understanding, I wish it to be understood that my invention is not limited to the specific forms of illustration, or to the specific examples, or to my present understanding thereof as many changes of omission, addition, and substitution of equivalents, may be made, by those skilled in the art, without departing` from the essential spirit of my invention, particularly in its broader aspects. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. An impulse-counting timer-assembly, comprising a pair of serially connected capacitors, one capacitor being considerably larger than the other; a unidirectional voltage-source for charging said capacitors; a charging rectifier in series with the larger one of said serially connected capacitors; a discharging rectifier in shunt around both said charging rectifier and said large capacitor; electro-responsive control-means for, in effect, periodically alternately establishing, and substantially opening, a discharging-circuit for said smaller capacitor, said discharging-circuit including said discharging rectifier; asource of counter-controlling voltage-peaks ior controlling said electro-responsive control-means; and an electro-responsive controlled device which is responsive to the total accumulated voltage of said larger capacitor.

2. An electronically timed square-wave generator, comprising a pair of trigger-tubes of the sustained-discharge type; means for unidirectionally energizing the anode-cathode circuits of said trigger-tubes; the anode-cathode circuit of at least one of said trigger-tubes including a means containing resistance, and output-leads associated with said resistance-means, for supplying an output-voltage having a magnitude which is responsive to the :firing or non-firing of said trigger-tube; a commutating capacitor so interconnected between the anode-cathode circuits of the two trigger-tubes as to extinguish one trigger-tube when the other trigger-tube fires; a separate pair of serially connected capacitors associated with each one of said trigger-tubes, one capacitor of each pair being very much the larger; means for connecting the larger capacitor across the control-circuit of the associated trigger-tube; a unidirectional voltage-source for charging both pairs of serially connected capacitors; a charging rectifier in series with each of the larger capacitors of said pairs; a discharging rectifier in shunt around both the charging rectifier and the larger capacitor of each pair; electro-responsive means for, in effect, periodically alternately establishing, and substantially opening, a discharging-circuit for each of the smaller capacitors of said pairs, each discharging-circuit including the associated discharging rectifier; and a source of counter-controlling voltage-peaks for controlling said electro-responsive control-means.

3. A step-counting timer-assembly, comprising a step-measuring capacitor; means for applying, to said step-measuring capacitor, a succession of timed, discrete voltage-increments of the same polarity; and an electro-responsive controlled device which is responsive to the total accumulated voltage of said step-measuring capacitor, the critical response-voltage of said 22 controlled device being such as to fall in some intermediate portion of the final step to which the controlled device responds.

4. A synchronized timer, comprising the combination, with an alternating-current input-circuit, of a step-measuring capacitor; electro-responsive control-means. responsive to the alternations of said input-circuit, for applying, to said step-measuring capacitor, a succession of timed, discrete voltage-increments of the same polarity; and an electro-responsive controlled device which is responsive to the total accumulated voltage of`said step-measuring capacitor, the critical response-voltage of said controlled device being such as to fall in some intermediate portion of the final step to which the controlled device responds.

5. A counter-controlled inverter-rectifier assembly comprising a plurality of rectifier-tubes of the sustained-discharge type; an input-circuit associated therewith; an alternating-current output-circuit associated therewith; and a plurality of step-counting timer-assemblies for determining the times ci operation and non-operation of the rectifier-tubes, and thus determining the frequency and the phase-positions of the outputcircuit: each step-measuring timer-assembly comprising a step-measuring capacitor; means for applying, to all of the step-measuring capacitors, a succession of timed, discrete voltage-increments of thel same polarity; and a separate electro-responsive controlled device which is responsive to the total accumulated voltage oi each step-measuring capacitor, the critical responsevoltage o f each controlled device being such as to fall in some intermediate portion of the iinal step to which the controlled device responds.

6. A counter-controlled electronic frequencychanger assembly, comprising an alternatingcurrent input-circuit; an alternating-current output-circuit; a plurality of positively and negatively connected groups of rectier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to the alternations of said input-circuit, for producing a succession of timed, discrete countercontrolling impulses; and tube-controlling means, associated with said rectifier-tubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timer-assemblies, responsive to said counter-controlling impulses, for also controlling said rectier-tubes.

'7. A counter-controlled electronic frequencychanger assembly, comprising an alternatingcurrent input-circuit; an alternating-current output-circuit; a plurality of positively and negatively connected groups of rectiiier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electroresponsive control-means, responsive to the alternations of said inputcircuit,for producing a succession of timed, discrete counter-controlling impulses; and tube-controlling means, associated with said rectifier-tubes, and comprising a pluralityof input-frequency tube-controlling means, and a plurality of output-frequency square-wave generators, each square-wave generator comprising step-counting means, responsive to said counter-controlling impulses, for alternately raising and lowering a control-voltage of said rectifier-tubes.

8. A counter-controlled electronic frequencychanger assembly, comprising an alternatingcurrent input-circuit; an' alternating-current output-circuit; a plurality of positively and negatively connected groups of rectifier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to the alternations of said input-circuit, for producing a succession of timed, discrete counter-controlling impulses; and tube-controlling means, associated with said rectier-tubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timerassemblies, responsive to said counter-controlling impulses, for so controlling said rectier-tubes that each half-wave of the output can be ad- .iusted so as to have the same number of rectier conducting-periods, in the same phase-relation to the input, deilning a rectifier conductingperiod as the time-interval between successive crossing-points of the voltage half-waves of the input-phases which are effectively applied to the several rectifier-tubes.

9. A synchronized timer comprising the combination, with a three-phase input-circuit, of means for obtaining a positive counter-controlling impulse and a negative counter-controlling impulse for each cycle of each phase of the input-circuit, in timed, predetermined phase-relation thereto; circuit-means for combining said counter-controlling impulses in a single circuit; counter-means for selectively responding to a predetermined integral number of counts of said positive counter-controlling impulses; and counter-means for selectively responding to a predetermined integral number of counts of said negative counter-controlling impulses.

10. A synchronized timer comprising the combination, with a three-phase input-circuit, of means for obtaining two timed, discrete, positive counter-controlling impulses from each cycle of each phase of the input-circuit; circuit-means for combining said counter-controlling impulses in a single circuit; and counter-means for responding to a predetermined integral number of counts of said counter-controlling impulses.

l1. A counter-controlled electronic frequencychanger assembly, comprising a polyphase inputcircuit; an alternating-current output-circuit; a plurality of positively and negatively connected groups of rectifier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to all of the inputphases, for producing a succession of timed, discrete counter-controlling impulses; and tubecontrolling means, associated with said rectiertubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timer-assemblies, responsive to said counter-controlling impulses, for also controlling said rectifier-tubes.

12. A counter-controlled electronic frequencychanger assembly, comprising a polyphase inputcircuit; an alternating-current output-circuit; a plurality of positively and negatively connected groups of rectifier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to all of the inputphases, tor producing a succession of timed, discrete counter-controlling impulses; and tubecontrolling means, associated with said rectiertubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of output-frequency square-wave generators,

each square-wave generator comprising stepcounting means, responsive to said counter-controlling impulses, for alternately raising and lowering a control-voltage of said rectifier-tubes.

13. A counter-controlled electronic frequencychanger assembly, comprising a polyphase inputcircuit; an alternating-current output-circuit; a plurality of positively and negatively connected groups of rectier-tubes oi the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to all of the inputphases, for producing a succession of timed, discrete counter-controlling impulses; and tubecontrolling means, associated with said rectifiertubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timer-assemblies, responsive to said counter-controlling impulses, for so controlling said rectiiier-tubes that each half-wave of the output can be adjusted so as to have the same number of rectifier conducting-periods, in the same phase-relation to the input, dening a rectifier conducting-period as the time-interval between successive crossing-points of the voltage half-waves of the input-phases which are effectively applied to the several rectifier-tubes.

14. The combination, with a three-phase input-circuit, of an electronically timed squarewave generator, comprising a pair of triggertubes of the sustained-discharge type; means for unidirectionally energizing the anode-cathode circuits of said trigger-tubes; the anode-cathode circuit of at least one of said trigger-tubes including a means containing resistance, and output-leads associated with said resistance-means, for supplying an output-voltage having a magnitude which is responsive to the ring or nonring of said trigger-tube; a commutating capacitor so interconnected between the anode-cathode circuits of the two trigger-tubes as to extinguish one trigger-tube when the other triggertube res; a separate pair of serially connected capacitors associated with each one of said trigger-tubes, one capacitor of each pair being very much the larger; means for connecting the larger capacitor across the control-circuit of the associated trigger-tube; a unidirectional voltagesource for charging both pairs of serially connected capacitors; a charging rectifier in series with each of the larger capacitors of said pairs; a discharging rectifier in shunt around both the charging rectifier and the larger capacitor of each pair; means for obtaining a positive counter-controlling impulse and a negative countercontrolling impulse from each cycle of each phase of the input-circuit, in timed, predetermined phase-relation thereto; circuit-means for combining said counter-controlling impulses in a single circuit; electro-responsive means, selectively responsive to said positive counter-controlling impulses, for, in effect, periodically alternately establishing, and substantially opening, a discharging-circuit for the smaller capacitor of one of said pairs; and electro-responsive means, selectively responsive to said negative countercontrolling impulses, for, in eiect, periodically alternately establishing, and substantially opening, a discharging-circuit for the smaller capacitor of the other one of said pairs; each discharging-circuit including the associated discharging rectifier.

15. A counter-controlled, polyphase, electronic frequency-changer assembly, comprising a polyphase input-circuit; a polyphase output-circuit;

a plurality of positively and negatively connected groups of rectiiier-tubes of the sustained-discharge type, for interehanging power between said input and output circuits; electro-responsive control-means, responsive to all of the inputphases, for producing a succession of timed, discrete counter-controlling impulses; and tubecontrolling means, associated with said rectiiiertubes, andcomprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timer-assemblies, each responsive to said counter-controlling impulses, one of said timer-assemblies counting the same number of impulse-counts for controlling the durations of the rectiiioation-permitting periods of both the positively and negatively connected groups of the rectifier-tubes associated with one of the output-phases; and the other timer-assemblies counting the number of impulse-counts f or spacing the successive output-phases.

16. A counter-controlled, polyphase, electronic frequency-changer assembly, comprising a polyphase input-circuit; a polyph'ase output-circuit; a plurality of positively and negatively connected groups of rectifier-tubes of the sustained-discharge type, for interchanging power between said input and output circuits; electro-responsive control-means, responsive to all of the inputphases, for producing a succession of timed, discrete counter-controlling impulses; and tube-controlling means, associated wth said rectifiertubes, and comprising a plurality of input-frequency tube-controlling means, and a plurality of step-counting timer-assemblies, each responsive to said counter-controlling impulses, one of said timer-assemblies counting a predetermined number of impulse-counts for controlling the duration of the output-frequency rectiiication- Ipermitting period of one of the tube-groups of the pair of positively and negatively connected tube-groups which are associated with a iirst one of the output-phases; another timer-assembly counting a larger number of impulse-counts for controlling the duration of the output-frequency rectification-blocking period of the same tubegroup; two other timer-assemblies counting the proper number of impulse-counts for spacing the rectification-permitting vand rectication-blocking periods of the other one of the tube-groups of said pair of positively and negatively connected tube-groups which are associated with said iirst output-phase; and the remaining counter-assemblies counting the proper number of impulsecounts for spacing the successive output-phases.

17. A cycloconverter for converting from an input-circuit of one frequency to an output-circuit of a lower frequency, comprising a plurality of positively and negatively connected groups of rectiiier-tubes of the sustained-discharge type, for interchanging power between said inputand output circuits; electro-responsive control-means, responsive to the alternations of said input-circuit, for producing a succession of timed, discrete counter-controlling impulses; and tubecontrolling means, associated with said rectifiertubes, and comprising means for supplying relatively low-voltage input-frequency rectifier-firing peaks to the control-circuits of the several rectifier-tubes, means for supplying relatively highervoltage input-frequency, inverter-firing peaks to the control-circuits of the several rectier-tubes, and a plurality of square-wave generators for supplying substantially square-topped outputfrequency waves to the control-circuits of the several groups of rectiiier-tubes, for alternately permitting and blocking the rectifier-firings, while always permitting the inverter-flrings, at least one of said square-wave generators comprising: a pair of trigger-tubes of the sustaineddischarge type; means for unidirectionally energizing the anode-cathode circuits of said triggertubes; the anode-cathode circuit of at least one of said trigger-tubes including a means containing resistance, and output-leads associated with said resistance-means, for supplying an outputvoltage having a magnitude which is responsive to the firing or non-firing of said trigger-tube; a commutating capacitor so interconnected between the anode-cathode circuits of the two trigger-tubes as to extinguish one trigger-tube when the other trigger-tube res; a separate pair of serially connected capacitors associated with each one of said trigger-tubes, one capacitor of each pair being very much the larger; means for connecting thelarger capacitor across lthe control-circuit of the associated trigger-tube; a unidirectional voltage-source for charging both pairs of serially connected capacitors; a charging rectifier in series with each of the larger capacitors of said pairs; a discharging rectifier in shunt around both the charging rectiiier and the larger capacitor of each pair; and electro-responsive means, responsive to the discrete counter-controlling impulses, for, in eiiect, periodically altern'ately establishing, and substantially opening, a discharging-circuit for each of the smaller capacitors of said pairs, each discharging-circuit ini cluding the associated discharging rectifier.

, DAVID BARTLETI. 

